The present invention relates to a coil device having a core, and a core fixing member for fixing a core to a case of the coil device.
A reactor is a passive element which gives an inductive reactance to an alternating component of a signal, and is used, for example, in an inverter circuit, an active filer circuit or a DC step-up circuit. A reactor is also used for a DC step-up and step-down converter which is a key device of a driving system in a hybrid vehicle or an electric vehicle which has been brought in practical use in recent years. In general, a reactor having a relatively large capacity used for an electric vehicle is configured such that a core which is a magnetic material formed in a ring shape and a coil wound around the core are accommodated in a radiation case. In order to prevent magnetic saturation, in general, a structure (a divided core structure) in which the core is divided into a plurality of pieces arranged in a plane which is perpendicular to a magnetic flux and a gap member is inserted into a space between the divided surfaces to adhere the divided pieces to each other is employed.
Since the core generates heat due to an energy loss, such as an iron loss, it is important to secure sufficient heat conduction from the core to the radiation case. Furthermore, regarding a reactor used for a DC step-up and step-down converter, vibration and noise are caused by magnetostriction of the core or the electromagnetic attraction because charge and discharge of the energy are repeated. When a divided core is used, the vibration strongly occurs particularly in a direction perpendicular to the gap surface of the divided core.
Japanese Patent Provisional Publication No. 2010-123927A (hereafter, referred to as patent document #1) discloses a fixing member of a leaf spring type configured to hold tightly a core in a radiation case. The fixing member, which is made from a metal plate and is elastically deformable, presses the core against bottom and side faces in the inside of the radiation case. By employing such a fixing structure (a metal touch structure) for causing the core to closely contact the radiation case, it becomes possible to secure a suitable heat radiation property. However, in the reactor having the metal touch structure, the core directly contacts the radiation case. Therefore, in this case, the vibration caused by the core propagates to the case without attenuation, and thereby a relatively large noise is caused at the time of activation.
Japanese Patent Provisional Publication No. 2009-26952A (hereafter, referred to as patent document #2) proposes a fixing structure (a floating structure) in which a core is supported with a stay without contacting a radiation case. A conventional stay disclosed in patent document #2 is formed by bending a slender rectangular metal plate in a shape of a letter ‘L’. The core is configured by divided core pieces (magnetic materials) which are arranged in a shape of a ring and are integrally coated with resin by injection molding. At the time of injection molding (insert molding), an end of the stay is buried in the resin coating the core and is fixed to the core. Furthermore, the other end of the stay is provided with a fixing part having a shape of a flat clip plate so that, by fixing the fixing part to the radiation case with a bolt, the reactor body is fixed to the radiation case via the stay in the state where the reactor body floats from the radiation case. Since such a fixing structure does not cause the core to directly contact the radiation case, it becomes possible to reduce the vibration propagating from the core to the radiation case and thereby to reduce the noise caused by the reactor.